(a) Field of the Invention
This invention relates to a heavy duty power transmission V-belt formed by engaging and securing a plurality of blocks to one or more tension members.
(b) Description of the Related Art
There have been conventionally known heavy duty power transmission V-belts in which a plurality of blocks are securely engaged to one or more tension members using their matingly engaged structure, as disclosed in, for example, Japanese Unexamined Utility Model Publication No. 1-55344 (Japanese Examined Utility Model Publication No. 7-29332), Japanese Unexamined Utility Model Publication No. 6-69490 or Japanese Unexamined Patent Publication No. 5-272595. These V-belts are used, for example, in the field of continuously variable transmissions. In these V-belts, for the purpose of ensuring their flexibility, the securement of each block to the tension member is made not by adhesion but by physical engagement (mating engagement).
A belt of this kind includes, for example, a pair of right and left tension members aligned widthwise of the belt. Each tension member is provided with a set of upper receiving parts in the top and a set of lower receiving parts in the bottom, each set of the receiving parts consisting of a plurality of elongated recesses aligned lengthwise of the belt in pairs of oppositely disposed upper and lower elongated recesses. In the belt, as shown in FIGS. 26 and 27, each block 10 is formed at both lateral sides with indented slot-like fitting parts 12 and 12 (only one shown in the figures) each for receiving the associated tension member (not shown). The upper face of each fitting part 12 is provided with an upper ridge 14 as an upper inserting part, while the bottom face thereof is provided with a lower ridge 15 as a lower inserting part. Each block 10 is securely engaged to both the tension members by fitting the tension members into the associated right and left fitting parts 12 and 12 of the block 10 by press insertion.
In a proposed example disclosed in Japanese Patent Publication No. 3044212, the back of the fitting part of each block in the direction of insertion of the tension member is formed at the lower corner with a lower abutment surface inclined to become deeper with the approach to the top. When the lower abutment surface is formed downward from the pitch line or above, a relationship β−3<α<β+3 is established between a lower abutment surface angle α made by the lower abutment surface and a vertical plane along the length of the belt and a belt side face angle β made by the contact part of each block side surface with a pulley and the vertical plane. On the other hand, when the lower abutment surface is formed downward from below the pitch line, another relationship α≦β is established between them. According to this proposed example, the proper relationships hold between the angle of a lower abutment part of the side surface of the tension member facing to the back of the fitting part of the block and the angle of the lower abutment surface of the block. This suppresses the occurrence of local wear, resulting in enhanced durability and reduced noise of the belt.
In the V-belts of this kind that includes the above proposed example, each block is formed of a complex of a reinforcement and a resin part. The reinforcement is made of a high-strength material such as metals including an aluminum alloy or steel, and is used to bear loads applied to the block. The resin part is used to form the contact part of the block with the pulley and the fitting parts of the block with the tension members.
The above proposed example, however, does not completely satisfy the demand for further enhanced performance and extended scope of application of the belt, and has room for improvement. In particular, when the belt is run at high speeds, there arises a problem that the block may be broken for the following reasons:
(1) At the high-speed running of the belt, each block undergoes severe vibration on the tension members to take loads from the tension members.
(2) When the belt contacts with the pulley at high speeds, the contact surfaces of each block with the pulley take heavy shock loads from the pulley.
(3) Each block has contact surfaces that are located at both ends of each of the upper and lower beams and will be points of application of force, and therefore each of the upper and lower beams takes the form of a bilateral cantilever beam. In this case, the root of each cantilever section receives the maximum bending moment. Therefore, stresses concentrate on the roots of the upper and lower cantilever beams, from which portions failure is likely to occur.
(4) In addition, it is difficult that edges of the resin part of each block forming the root ends of the upper and lower inserting/receiving parts of the upper and lower beams combine a form suitable for engagement with the tension member and a form that can avoid stress concentration. Therefore, stresses concentrate on the edges of the resin part so that the resin part may be damaged from any of them and produce a crack. When the crack reaches the reinforcement, the reinforcement may be broken beginning at the crack, resulting in fracture of the upper or lower beam of the block.
Specifically, as shown in FIGS. 26 and 27, the back of the fitting part 12 of each block 10 in the direction of insertion of the tension member is formed with an innermost abutment surface 20, edges E and E are formed at the meeting points between the innermost abutment surface and both the upper and lower ridges (inserting parts) 14 and 15. Stress concentration on the edges E and E invites the occurrence of a crack in the resin part. When the crack produced in the resin part reaches the reinforcement, the reinforcement also produces a crack beginning at the crack in the resin part, and finally invites the fraction of the upper or lower beam.
An object of the present invention is to prevent as much as possible each block of a heavy duty power transmission V-belt with one or more tension members, such as shown in the above proposed example, from producing failure at the high-speed running of the belt, by improving the structure of the fitting part of the block.